Explosively actuated driving



Jan. 12, 1960 c. J. DE cARo 2,920,563

EXPLOSIVELY ACTUATED DRIVING Filed Feb. .9, 1955 -/9 Um W a z/J g 2 24C'ha'rles 6211:221 3 ATTORNEY EXPLOSIVELY ACTUATED on Charles J. DeCaro, Cleveland, Qhio, assignor, by mesne assignments, to 01in MathiesonChemical Corporation, a corporation of Virginia Application February 9,1953, Serial No. 335,925 Claims. (Cl. Elm-38)- This invention relates totools and more specifically to the driving of fasteners such as pins andstuds into objects of steel, masonry, concrete, wood and the like by useof an explosive actuated tool.

Heretofore, driving and gas obturating means for such projectile typesof fasteners have taken various forms and particularly that of acylinder or piston of metal use of which has not only the disadvantageof interposing a heavy body between the explosive charge and thefastener with attendant diminution of driving power but also thedisadvantage of requiring costly precision manufacturing methods toprovide the close tolerances and fit needed to insure a minimum ofclearance but no binding between the bore of the firing tool and theside wall of the obturator. Such. means have also been provided in theform of a cup shaped piece of metal but this, in common with theaforementioned piston, suffers from the disadvantage that the muzzle ofthe barrel of the tool must have an internal shoulder and the like forcapturing the cup, or the piston, which may then be retrieved for reuse.Further, the side walls of the cup bearing forcefully on the bore of thebarrel cause even greater barrel wear than the metal piston. To retrievethese pieces has necessitated after each shot tedious dissembly of partof the tool which must then be reassembled before the next drivingoperation is commenced. This tedious procedure also suffers from thedisadvantage that workmen using such tools at a considerable heightabove the ground not infrequently drop the piston or cup parts and onaccount of the loss of these and other coacting parts the work ofdriving the fasteners must be halted until replacements can be had.

Another known type of obturating means takes the form of a convolutelywound strip of paper wrapped around the threaded side of a fastener butthis is not only most uneconomical but also rather dangerous sincefragmentation of the paper or fiber tube produces flying particles whichendanger the eyes of the tool operators and may even cause a violentreaction on the tool, if part of the tube remains as an obstruction inthe barrel.

Attempts at use of various other obturators such as the wads commonlyemployed in cartridges for firearms have not been too satisfactorylargely because of the vastly' different pressure and temperatureconditions encountered in driving fasteners with explosives as comparedto projection of bullets or shot in the ammunition art where wads ofsuch material as rubber, cork, paper, sawdust, fiber, hair and strawsometimes admixed with one or more binders such as linseed oil,stearine, pitch, paraffin, or asphalt are well known. There have alsobeen disclosed in the art wads for use in firearms consisting of discsor shallow cups of thin material both metallic and nonmetallic but suchforms of gas check fail to perform properly and consistently in powderactuated tools because such a wad tends to tip and misalign itselfbefore seating itself on the rear portion or base of a fastenerprepositioned ahead of the wad and at the same time the wad has atendency to lap over the base of the fastener 2,920,563 i atented Jan.12, 1960 and force itself between the tool bore and the fastener andinvariably causes fouling of the threads of a threaded fastenerparticularly where the'wad consists of a soft metal such as lead orcopper.

The present invention has for one of its objects the provision inconnection with explosive driven fasteners of a new and improved memberfor sealing off the gaseous products of combustion of the propellentpowder charge behind the fastener element in order that the availablepower of the charge may be substantially fully and substantiallyuniformly utilized while barrel erosion is reduced particularly at highpropellent loads.

Another object of the invention is the provision of a novel gas check orobturating means made of a light cohesive plastic material having alubricating effect in the barrel of the tool from which the fastenersare projected and incapable of decomposition to form corrosive productsin the barrel during explosion of the propellant.

Another object of the invention is to provide means for keeping theextremely high pressure, high temperature propellent gases away from themetal fastener so as to powder containing cartridge and the rear endportion of a fastener of the type described and capable of bringingabout the desired obturation regardless of variations between the borediameter of the tool barrel and the calibre of the fastener and under avariety of spacing conditions between the fastener and explosivecartridge in the tool barrel.

Another object is to provide a plastic driver and gas check conformableunder pressure to the bore of the tool barrel notwithstanding certainvariations in the bore and certain differences between thecircumferential shape of the bore and the gas check.

A still further object is to provide a new and improved fastener driverand gas check structure made'of polyethylene or equivalent materialwhich will overcome the defects of prior art devices. I

Other objects and advantages of the present invention will be obviousfrom the following description of several embodiments and from theaccompanying drawing in which:

Figure l is a side view of one embodiment of the invention.

Figure 2 is a rear view of the embodiment shown in Figure 1.

Figure 3 is a side view partly in cross section showing anotherembodiment of the invention.

Figures 4 and 5- are side views also partly in 'cross section showingtwo additional embodiments of the invention.

Figure 6 is a fragmentary side view including a fastener, a cartridgepartially in cross section and one embodiment of the obturating means ofthis invention positioned at the breech end of a tool barrel shown incross section.

Figure 7 is a side view illustrating a still further embodiment of thisinvention in assembly with a fastener and explosive cartridge. 5

Figure 8 is a perspective view showing still another embodiment of theinvention. g

In accordance with the present invention, generally stated, there isprovided for disposition between the rear end portion of a projectableor fastener element and a propellent explosive and obturatingdrivingmember formed of plastic material having suitable form retainingrigidity together with elastic properties and resistance to rapiddeterioration by burning. The gasrobturating driving means of thisinvention is preferably formed of a;

' ber is preferably made of an elastolene such as a normally solid toughpolymer of an olefinic hydrocarbon. A solid polymer of ethylene of thetype formed at high temperature and pressure as disclosed in US. PatentNos. 2,153,553 and 2,188,465 or 2,342,400 is particularly suited forthe: purpose. This plastic known specifically as polyethylene was foundtobe the most suitable material when given the forrhand structuredisclosed herein for the purpose ofthis invention. The polyethylene maybe either oriented or unoriented. Solid polymers having a molecularweight in excess of 10,000 are preferred inasmuch as the highermolecular weight poly-- ethylene remains tough and flexible though hardover a wide range of temperatures and is form stable near the softeningtemperature which lies in therange from 110 to 200 C. For greatestimmunity from cracking of the stress plastic the polymer should have ashigh as possible a molecular weight. Polyethylene with an averagemolecular weight of about 18,000 is suitable fo the purposes of thisinvention.

While it is contemplated that thedriving and gas check member'be madefrom a plastic composition essentially polyethylene or its equivalent',the plastic may be compounded with one or more of polyisobutylene tosome extentto raise the heat softening point and fiexi-- bility, somewax, carbon black, various coloring agents generally inorganic pigmentssuch as titanium dioxide and the like, and finely divided calciumcarbonate to further raise the softening point and toughness without besuch as to be capable of filling the space in the bore between thefastener and propellant under the compressi ve force of the gases whenthe propellant charge is fired. A generally massive or cylindricalstructure characterized by axial thickness or length sufficient forobtainment of obturating lateral distention of the structure un-' derthe axially compressive force of the propellant is well adapted for thedriving means of this invention For best operation it ispreferred thatsuch structure be additionally providedwith. a hollow posterior sectionhav ing a recess facing the rear.

Inthe embodiment shown in Figures 1 and 2 the gas check or drivingmember consists of a'generally cylindrical molded body of polyethylene.tion 1 of the body is essentially a solid section of greatest diameter,somewhat less than that of the bore of the tool barrel, and is adaptedto provide obturationby lateral or diametral elongation or expansionunder the axial compression which portion 1 undergoes between 'therearportion of a fastener and the pressure of the gases of the propellantexplosive acting axially. As compared to the relatively thin posteriorportion 2, portion 1 is a bulky section suitable for lateral distentionunder compressive forces. The rearmost portion 2 of this embodiment ofthe invention'is acoaxial section of lesser diameter than part 1- tofacilitate inserting the gas check into the open effective moistureresistant cartridge closure for retaining the propellant powder thuseliminating the need for a separate top wad cartridge closure. Posteriorsection 2 is a hollow section having a conical concavity or recess 3beginning at the rear face of the gas check and tapering to convergenceat a point short of the front face 5 of the cylindrical body ofpolyethylene. The periphery of the front face 5 is provided with achamfer 4 in order that propellant powder cartridges loaded with theplastic gas check of this invention may feed more easily into the breechof the tool barrel especially from an automatic feeding device of themagazine or cartridge clip type.

The embodiment of Figure 3 differs from that of Figures 1 and 2 in theprovision of a shallow concavity '6 in the front face of the anteriorsection 1 while leaving the posterior section 2, the rear concavity 3and the front chamfer 4 of the prior embodiment unchanged. Although theembodiment of Figure 3 may be expected to handle with more difficultyin'feeding than the embodi- .ment of Figures 1 and 2, the frontconcavity 6 enhances the elastic lateral expansibility of the anteriorcompres vided, its thickness should not greatly exceed themaximum-clearance usual between the rear portion of the fastenerand the;bore of the tool barrel. Otherwise the plastic material of the gas checkdriver is likely to extrude around the fastener instead of forming asemi-rigid resilient body behind the fastener; With the modification ofa front flange together with the coaxial rear portion of reduceddiameter, the embodiment of Figure. 3 serves as a means of connecting acertain type of fastener and an explosive cartridge as'an integral unitwhich is desirable on certain construction projects employing explosivedriven fasteners. V

In the embodiment illustrated in Figure 4 the anterior portion 7 takesthe'form of the ogival portion or nose of a bullet. The posteriorsection 2 like the foregoing embodiments is of reduced diameter and isprovided with a tapering recess 3 which improves'the ohturationobtainable with the gas check of this invention during the initial stageof each driving shot. This embodiment is virtually -a synthetic plasticbullet with a hollow heei and has the advantage of permitting handling,loading and feeding on conventional ammunition machinery. This formofgas, check is especially advantageous where attachment between thefastener and explosive cartridge isv not desired but where easy feedingof the cartridges as from a magazine'clipis required.

The anterior portridgewhere the polyethylenebody'also acts as a veryIntheembodimentshdwn in Figure 5-, reference char- -acters8 and'9'iden'tify annular protrusions or flanges having adiameter'somewhatin' excess'of the bore diameter so as to better holdthe plastic gas. check in the tool during loading. Flanges 8 and 9 areportions whichwiil provide initial 'obturation on loading and areadapted to. engage withfany enlarged bore sections found in certaintypes of tool barrels. Theannular recess it) in combination with andbetween theannular protrusions serves to prevent jamming and bindingwhich would make loading difiicult and also prevents unnecessariiy highobturating forces during firing; -To facilitate coupling with apropellent powder cartridge posterior sec tion 2 is of reduced diameter;and to initiate the obturating effect as soon as possible posteriorportion 2 is provided with a recess 3. r 1

In Figure 7 the gas check driving device of this invention is shown 'inthe form, of a connector between a fastener 21 and a cartridge 17. Thefastener is of the type having the usual enlarged rear portion 22adapted to fit the bore of the tool barrel with clearance within theusual commercial tolerances and having an internal thread for connectionwith other devices as required for the construction work being done. Theforepart of the fastener is provided with a cap-like centering andguiding means 20 of the type shown in the drawing. In this instance thegas check driver comprises a relatively bulky or massive mid portion 11adapted to undergo lateral distension under axial compression, couplingmeans 23 on the front of part 11 for connection with the fastener head22, and a posterior section 24 adapted to connect with a rimfirecartridge 17 containing a propellant material 26 and a primer material25. In this embodiment the gas check serves as an element in a completefastener-propellent cartridge unit.

In the embodiment of Figure 8 the driver consists of a solid circularcylinder 12 of polyethylene having no concavities but characterized by asomewhat greater length of plastic than the prior embodiments in orderthat adequate lateral distension may be obtained. With certain types ofpropellent cartridges, this form, as well as some of the others, may beadvantageously secured to the back face of a fastener by interlockingmeans or an adhesive, for example.

With respect to the several embodiments just described it is to be notedthat the provision of a thin walled hollow cup shaped body alone withthe recess facing either the fastener or the propellant would beundesirable for lack of form retaining rigidity, difficulty in loading,and inability .to provide the degree of obturation obtained by means ofmy invention under the conditions encountered.

In Figure 6 there is shown a gas check of the type illustrated inFigures 1 and 2 having a nose portion 1 in the bore 14 of tool barrel 13facing the fastener 15 and rear portion 2 fixed as a closure in themouth of an explosive cartridge 17 of the rimfire type disposed in thebreech of the barrel 13. The stud-fastener 15 pre-positioned in the bore14 and desirably spaced ahead of portion 1 of the gas check to furthercontrol the power is provided at the front end with a plastic centeringand guiding means or point cap 20 affixed thereto of the aforementionedtype which aids in positioning the fastener axially as Well as centeringit and guiding it in the bore of the tool barrel. The rear end of thestud consists of an externally threaded head 16 having a diametergreater than that of the shank portion of stud 15. Initiation of thedriving operation occurs by striking the rim of cartridge 17 with afiring pin projectable through the aperture 19 provided in the breechlock 18 attached at the rear end of barrel 13. Any explosive actuatedtool of the type suitable for projection of studs and pin fastenersshown and described may be utilized.

The minimum axial thickness of plastic needed to insure the lateraldistention to accomplish obturation will vary with the molecular weightof the polymer, 'with the type and amounts of the aforementionedadditives and coloring agents or fillers, and with other factors.

Polyethylene (or any equivalent resilient synthetic organic plastic) isadmirably suited for the purpose of this invention. In the first place,it is elastically deformable under compression very much like rubber andwill compress longitudinally under the axial impact force of thepropellant with concomitant lateral distention to provide desiredobturation between fastener and propellant. But unlike rubber andcertain other plastics, it was found that polyethylene does not have thetackiness and relatively high coeflicient of friction of these materialswith respect to a smooth metal surface such as the bore of'the toolbarrel but on the contrary has self-lubricating properties even at thehigh temperatures of powder combustion due to its wax-like surface.Since an obturator coacts with the wall of the bore of the tool barrelas well 'as with the fastener and propellant, the cleansing andlubricating the softening tempeature.

action of the polyethylene driver is important to insure that excessivewear and fouling of the tool barrel is prevented though extraneouslubricant is not used. Furthermore, it was found that the polyethylenegas check does not form corrosive products of combustion under theextreme tempenature and pressure conditions which occur in the toolbarrel upon firing of the fastener. On the contrary, a thin protectivefilm of polyethylene is believed to be left on the surface of the boreof the barrel. Since the polyethylene plastic gas checking driver istough and coherent and not brittle, it was found that it will notdisintegrate like fiber or other plastics to leave a residue in thebarrel and flying fragments at the muzzle adjacent the work withattendant loss of obturation and danger and inconvenience to the tooloperator.

In its massive form especially, it was found that the gas check isespecially resistant to deterioration under the heat of the burningpowder since polyethylene has a slow burning rate at least to the extentthat such burning as does occur, does not impair gas sealing. Moreover,the consumed polyethylene of the thinner posterior section of the gascheck is believed to add to the driving power of the powder charge ofthe cartridge since at the high temperatures attained during explosionof the propellant powder particularly under sustained operation of thetool part of the polyethylene may decompose explosively which mayaccount in part for the disappearance of the thin sections of thepolyethylene wad. Further, it was found that in the massive sectionsfound in the gas check structure of this invention polyethylene issufficiently rigid to hold its shape and resist excessive shearing pastthe fastener and extrusion into the usual clearance space between thebarrel bore and the rear end of a fastener even at high propellantpowder loads without total loss of elasticity however (polyethylene maybe classed as semi-rigid becasue in stiffness it lies between.

the conventional categories of rigid and non-rigid plastics). Suchextrusion of the driving member would cause jamming, loss of obturationand driving power and fouling of any threads on the fastener. Stillfurther, although massive in form, the plastic gas check here describedis characterized by desired lightness and resulting low loss of drivingpower sincepolyethylene is one of the-lightest of all plastics having aspecific gravity of 0.92. The high differential in weight between thesteel fastener and the polyethylene check accentuates the static inertiaof the fastener to promote obturating deformation of the gas check.

As compared to polyethylene other resilient plastic materials do nothave the combination of properties and characteristics needed for thepurpose of this invention. Elastomeric plastics such as rubber,butyrates and vinyl resins and various plastics containing halogen atomsor sulfur leave acidic products of decomposition which in the presenceof moisture formed in the barrel after each firing of the tool corrodethe barrel. Still other plastics, such as ethyl cellulose for example,simply lack flexibility unless plasticisers are incorporated whichrender these materials less stable because of the tendency of theplasticiser to evaporate or separate out and also reduce Because of theabsence of plasticisers, the polyethylene gas check suffers no change indesirable properties on account of aging.

The plastic gas checking driver of this invention is preferably made byeither an injection or a compression molding process but fabrication byworking such as machining of extruded stock is also feasibleparticularly for an embodiment like Figure 8.

As an illustrative specific example of an embodiment of the inventionsuch as the type shown in Figures 1 and 2 found suitable for use in anexplosive actuated fastener driving tool there was molded a gas check ofa polyethylene known as Alathon No. 1 made by E. I. du Pont de Nemours &Company having an average molecular weight of 18,000. For a tool havinga barrel with a nominal bore diameter of 0.250 of an inch or not lessthan 0.2505 of an inch but not more than 0.2510 of an inch, the anteriorportion 1 was easily molded with a diameter within the narrow range from0.247 of an inch to 0.249 of an inch and a length in the axial directionof about 7 of an inch. The posterior or heel portion 2 protrudingcoaxially rearwardly from portion 1 by about A; of an inch was providedwith a recess of generally conical shape beginning with a diameter ofabout of an inch at the rear face of portion 2 and extending forwardlyinto the body of the gas check to an apex forming anangle of about '45".'While thinner sections of portion 2 were found to have disappearedafter the fastener was shot the major portion of the gas check wasintact and was ejected fromthe muzzle of the barrel of the tool withapop by theresidual' gases showing the check was still in good conditionto provide a gas seal though it has been subjected to the hightemperature and high pressure impact of the burning propellant powder.The ability to retain a gas sealing form immediately after a shotfacilitates trouble free ejection of the expendable plastic gas check ofthis invention; but, if pressure is gone, the wad drops out easily.

Since the tool barrels of the type described are commonly provided witha circular bore, only a circular cylindrical shape of obturator has beenreferred to herein, but other cross sectional shapes= canbe employedwith a given barrel provided the shapeselected-is capable ofdistendingto seal the bore. While the gas check of this invention hasbeen described with particular reference to explosive driven fasteners,it is obvious that the'polyethylene gas check device may have utilityand advantages in the ammunition and fire arms art.

As hereinbefore mentioned the. present gas sealing members are intendedfor use with metal pins, studs and the like fastener elements. The pinsare generally provided at the baselooking at such pins as a -projectilewith" a work holding head portion having a diameter approaching thediameter of the bore of the barrel of the tool. The studs similarly areprovided at the base or rear end portion with an externally orinternally threaded head portion of a diameter nearly that of the boreof the barrel. gas sealing means of this invention the externaldiameters of the holding head or threaded portions of such fasteners,typical ones of which are shown in Figures '6 and 7, may vary from theinternal diameter of the tool barrel by at least the usualinterchangeable fit tolerances'and need not be held to the extremelysmall tolerances that are so costly to maintain to avoid excessive gasbleed around the fastener element" particularly at higher propellantloads. A clearance on one side between barrel and fastener head portionas high as about 0.005 of an inch is permissible I with the gas check ofthis invention.

From the foregoing description, it is evident that various advantagesare obtained with the presentinvention. Use of the plastic drivingmember will allow manufacture'of' fasteners having the greater and morevariable commercial tolerances rather than the heretofore closetolerances needed to prevent excessive blow-by, Further, use of the gascheck of this invention makes possible more 'efiicient use of theavailable energy in any given unit of powder load. Another advantagesecured isthe reduction of barrel erosion and prevention ofdeterioration of the surface or surface coating of the fastener by thehot propellant gases. Still another advantage is that the obturating anddriving device of this invention provides desired constancy anduniformity of driving power and resultant accurate and dependableuniformity of penetration depth of the fastener independently of thevariable sealing effect between the rigid fastener, having transversedimensions varying within relatively wide tolerances, and the barreldiameter, which varies within manufacturing tolerances and with wear andtemperature changes occurring during operation. Furthermore, a

8 cleaner work surface is obtained after firing. Still other advantagesare that the plastic gas check serves in the dual capacity of a powderclosure for the explosive cartridge and as means of identifying themagnitude of the powder load inthe cartridge when the gas check iscolored in conformity with a color code.

While various specific embodiments .of the invention have been shown anddescribed herein, it will be understood by those skilled in theart thatchanges and modifications may be made without departing from the spiritand scope of the invention and that the invention is' notto be limitedthereby except insofar as set forth in the appended claims.

What is claimed is: 7

1'. An overpowder gas check member adapted for use in the bore of thebarrel of an explosive operated devicebetween a projectable member andthe explosive propellent'. powder comprising a body of a solidpolyethylenic polymer or the like olefinic plastic substance havingaself-lubricating surface and elasticity together'with sub stantialresistance to rapid deterioration and excessive plastic deformation allin the presence of the flame and pressure of the reaction products ofsaid powder, said substance having properties, including the aforesaid,generally similar to those of polyethylene of a molecular weight of atleast 10,000.

2. A driving member for use in the bore of the barrel 7 of an explosiveoperated device comprising the sole over 7 mercial tolerance, comprisingan elasticallydeformable When used in connection with the plastic bodyfree from plasticizer and of cylindrical configuration at least oneportion of which is a disk-shaped solid characterized by a diametersubstantially equal to that of the said bore and an axial thicknesssufficient to permit axial compression with concomitant obturatinglateral expansion of said portion under the impact force of the productsof combustion of the explosive propellent powder, said body formedessentially of a self-lubricating grade"- of' solid polyethylene havinga molecular weight of at least about 10,000 and suflicient to impart substantial' resistance against any tendency of said body to extrudeexcessively through said space along said pro ject'able' member duringdriving.

3. A propellent device for use in the bore 'of the barrel of anexplosive operated tool for driving studs having clearance space betweenat least the rear end of said stud and said bore within maximumcommercial tolerance,

said device comprising a cartridge case open at one end and having anexplosive powder charge therein, an elastically deformable cylindricaloverpowder closure in the open end ofsaid case, said closure having atleast one portion a disk-shaped solid being adapted to snugly engage theopen end of the case and having an axial thick ness sufficient to permitaxial compression with concomitant radial expansion under the impactforce of the productsof combustion of saidcharge, said closure conesisti'ngessentiallyof a self-lubricating grade of solid polyethylenefree from plasticizer'and extraneous lubricant and having a molecularweight not less than about a 10,000 and aver'aging about 18,000sutficient to'impart substantial resistance against the tendency of saidbody to extrude excessively through said space during driving.

4. An overpowder plastic gas check wad comprising a polyethylene cupadapted to.elastically distend laterally and constituting the sole meansof maintaining obturation behind a projectable element in the bore ofthe barrel of an explosive propellent operated device under the.

force of the propellentpowder in the direct presence of the combustionproducts of said propellant, there being clearance space between saidelement and said bore within maximum commercial tolerance, saidpolyethylene being solid and of a self-lubricating-grade having 'amolecular weight not less than about 10,000 and averaging about 18,000sufi'icient to impart substantial resistance against the tendency ofsaid wad to extrude excessively through said space during driving, saidcup having a massive solid anterior portion of a diameter that of saidbore and a hollow posterior forming a recess opening to the rearadjacent said powder, said anterior portion having a chamfered front endand being of a length forward of said hollow portion sufiicient to beaxially compressible to provide obturating expansion.

5. A plastic gas check member according to claim 1 comprising an axiallycompressible laterally expandable solid cylindrical portion having bothan anterior recess and a posterior recess, said member being formed ofpolyethylene of a molecular weight of at least 10,000.

6. The driving member of claim 2 wherein the cylindrical body has ashallow concavity in its front face and a relatively deep concavity inits rear face and wherein the axial length of polyethylene between saidconcavities provides the disk-shaped solid portions having an axialthickness of polyethylene sufiicient for axial compression withconcomitant obturating lateral expansion of said portion.

7. The driving member of claim 6 wherein the cylindrical body has areduced diameter at the rear to permit afiixing the member into themouth of a propellent containing cartridge case.

8. The driving member of claim 2 wherein the cylindrical body has abulky solid anterior portion and a hollow posterior portion, saidanterior portion having at least one integral annular protrusionconnected to an adjacent portion of lesser diameter, and said hollowposterior portion having a reduced diameter at the rear to permitafiixing the member into the mouth of an explosive propellent cartridgecase.

9. The wad of claim 4, wherein the chamfered front end forms an ogivalanterior portion having at least a portion of its diameter substantiallythat of the bore.

10. The wad of claim 9 wherein the hollow posterior portion has areduced diameter at the rear to permit aflixing the Wad into the mouthof a propellent containing cartridge case.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Scientific American, July 1934, page 42.

1. AN OVERPOWDER GAS CHECK MEMBER ADAPTED FOR USE IN THE BORE OF THEBARREL OF AN EXPLOSVE OPERATED DEVICE BETWEEN A PROJECTABLE MEMBER ANDTHE EXPLOSIVE PROPELLENT POWDER COMPRISING A BODY OF A SOLIDPOLYETHYLENIC POLYMER OR THE LIKE OLEFINIC PLASTIC SUBSTANCE HAVING ASELF-LUBRICATING SURFACE AND ELASTICITY TOGETHER WITH SUBSTANTIALRESISTANCE TO RAPID DETERIORATION AND EXCESSIVE PLASTIC DEFORMATION ALLIN THE PRESENCE OF THE FLAME AND PRESSURE OF THE REACTION PRODUCTS OFSAID POWDER, SAID SUBSTANCE HAVING PROPERTIES, INCLUDING THE AFORESAID,GENERALLY SIMILAR TO THOSE OF POLYETHYLENE OF A MOLECULAR WEIGHT OF ATLEAST 10,000.